1. Field of the Invention
This invention relates generally to dentistry, and more particularly, to a system of matching dental color for facilitating and improving restorative dental procedures.
2. Description of the Related Art
The prior art provides essentially three methods for determining the colors of teeth in dentistry. These include, visual matching against shade guide color standards, colorimetry, and photography. Visual matching systems that employ shade guide color standards constitute the predominant color matching system. With this known system, a practitioner visually matches the color of the patient's tooth that will be restored against a series of color standards. It is a significant problem with this known method that its success depends upon the color vision of the practitioner. In the practice of the known method, the practitioner first selects, by visual inspection, standard colors that exhibit, to his or her eye, a general match to the subject's tooth. Then, a final match is performed that requires excellent color matching ability on the part of the practitioner.
As intimated, this known method is flawed, as the quality of the resulting restoration is largely related to the skill of the particular practitioner, and his or her ability to detect small color differences in the final matching from among the closest color standards. In a study by Kuehi & Marcus (Color Res. Appl 4: 83-91, 1979), large differences in the ability to discriminate color was shown among plural subjects, such ability ranging from 0.5 to 6 CIE .DELTA.E units. These measurements are determined using the known CIE L*a*b* system described, for example, in Bilmeyer, F. W., Principles of Color Technology, 2nd ed., John Wiley, 1981.
The prior art has sought to overcome some of the problems associated with visual color matching systems by applying colorimetry technology to the measurement of tooth colors in the clinic. However, this effort has not achieved success. A colorimeter was marketed in the 1970's (Chromoscan from Stemdent, N.Y.), but the unit failed to achieve adequate color discrimination (O'Brien & Nelsen, J. Prosthet. Dent. 49: 63-66, 1989). A more recent effort to overcome the stated problems is described in U.S. Pat. No. 4,654,794 ("O'Brien"), and employs a spectrophotometer. However, the prototype results were disappointing.
There are two major technical obstacles to successful clinical implementation of calorimeters to the measurement of tooth colors. First, the measurement of the color of translucent objects, specifically including teeth, suffers from inaccuracies that result from so-called "edge effects." As light from the calorimeter enters the tooth for measurement, it is scattered sideways away from the edges of the light beam. This results in significant diminution in the magnitude of light signal that is returned to the sensor. The second problem relates to the application of the calorimeter probe to the surface of the teeth, since teeth are irregular in shape. Colorimeters are designed to achieve accuracy of color measurement on flat, opaque objects.
Finally, photography has been used to show the color of teeth in lectures and textbooks, but it is known to be extremely inaccurate in reproducing color. During the several stages of the photographic process, uncorrectable color shifts take place which render accurate and reliable color reproduction not to be feasible. Nevertheless, practitioners regularly send photographs of patients' teeth to dental laboratories to show the approximate color.
It is, therefore, an object of this invention to provide a system for accurately determining the color of the teeth of a dental patient, without complete color discrimination reliance on the practitioner.
It is another object of this invention to provide a method producing a reliable record of color difference between the teeth of a dental patient and a color standard.
It is also an object of this invention to provide a method of selecting from a plurality of color standards, a color standard corresponding to the closest color match to the tooth of a dental patient;
It is a further object of this invention to provide a method of selecting from a plurality of color standards, each having a respectively associated color parameter, a one of the color standards corresponding to the closest color parameter match to the tooth of a dental patient;
It is additionally an object of this invention to provide a method of selecting from a plurality of color standards, each having a respectively associated color characteristic, a one of the color standards corresponding to the closest color parameter match to the corresponding color characteristic of a test subject.
It is yet a further object of this invention to provide a system for determining the color composition of a tooth whereby a restoration material can be formulated in response thereto.
It is also another object of this invention to provide a method of estimating the color parameters of a tooth of a dental patient.